1. Field of the Invention
The present invention relates to a tubeless solar collector and, more particularly, to an inexpensive, durable, highly efficient, and easy to manufacture tubeless solar collector.
2. Description of the Prior Art
Recent large price increases and reduced availability of fossil fuel and public concern about the safety of nuclear reactors have led to a surge of interest in using the energy of the sun. Furthermore, solar energy represents the only totally non-polluting, inexhaustable energy source that can be utilized economically to supply our needs for all time.
In most practical applications utilizing solar energy, solar radiation is absorbed by a surface in a solar collector and the energy is transferred, in the form of heat, to a working fluid that is circulated through the collector. This heat is then used for water heating, building heating, operation of conversion devices such as absorption coolers, and other applications.
The solar collector is the essential item of equipment which transforms the solar radiant energy to some other useful energy form. However, the engineering design and analysis of solar collectors presents unique problems because of the intermittent and diffuse nature of the input energy.
The most economic way to collect solar energy appears to be with so-called flat-plate collectors. Flat-plate collectors can be designed for applications requiring energy delivery at moderate temperatures, up to perhaps 100.degree. C. above ambient temperature. Flat-plate collectors have the advantage of using both beam and diffuse solar radiation. They are mechanically simpler than the concentrating reflectors, orientation devices, or focusing collectors, and require little maintenance.
A typical flat-plate collector, using a liquid heat transfer fluid, includes an absorbing plate, which is generally of metal, and which has a highly absorbent coating on the outer surface thereof to maximize the absorption of solar radiation. To the other side of the absorbing plate is connected a plurality of tubes which are attached with a good thermal bond, the tubes carrying the heat transfer liquid. The absorbing plate and tubes are positioned in a surrounding frame to protect the components from atmospheric contamination. The frame typically includes insulation around the sides and back of the absorbing plate to minimize heat loss to the surroundings. Also included is one or more glass or plastic covers in front of the absorbing plate to reduce the outward heat loss from the absorber to the surroundings.
While such flat-plate collectors can furnish a significant portion of the energy needed to provide hot water for both domestic and commercial use and for the heating and cooling of buildings, several problems have prohibited the wide-scale implementation thereof. First of all, most solar collectors are complex, difficult to manufacture, and expensive. Such expense occurs as a result of the plural tubes required and the procedure required for bonding the tubes to the back of the absorber plate. Furthermore, in order to create turbulence in the fluid flowing through the tubes, to increase heat transfer from the plate to the fluid flowing therethrough, separate turbulators are added and this adds to the complexity and cost of the collector. If a tube begins to leak, the common practice is to simply seal it off and this decreases the efficiency and thermal performance of the collector. Furthermore, leaks in the tubes are commonplace so that the lifetime of common solar collectors is not great. Furthermore, most collectors are not highly efficient so that large sizes are required for the absorbing plate, presenting space problems and increasing manufacturing and installation costs.